Fast reactor designs use fuel rich in actinides. Metal-fueled reactors are limited in operating temperature because of the low melting points of the intermetallic compounds of the actinides. In order to raise the melting point of the actinide-rich reactor fuel and improve the fuel's mechanical properties, approximately 10% zirconium is added in some current designs.
One actinide-rich metal reactor fuel used in fast breeder reactors currently contains approximately 70% uranium, 20% plutonium and 10% zirconium, by weight.
Using zirconium in reactor fuels has several drawbacks. One of these drawbacks is related to the irradiation of zirconium, which produces Zr-93. This isotope has a half life of 1.5.times.10.sup.6 years. This long half life presents a problem for waste disposal, in that assured isolation of the waste from the environment is required for millions of years.
Another drawback is that zirconium dilutes the fuel, which necessitates the use of a larger reactor core to produce the same amount of power.
Another drawback to using zirconium is the neutron penalty. The zirconium will absorb neutrons, which wastes fuel. Therefore, more fuel must be used for the same amount of power production.
A further drawback to using zirconium is that the relatively large volume of zirconium waste must be disposed of in an expensive geologic repository. The zirconium also weakens the fuel rod, lowering its operating temperature.